Solar Powered Hot Tub

This summer I collaborated with three friends on the design and installation of a grid-tied, battery backed 5.6KW, 24 panel photovoltaic array on a 260 acre ranch near Bailey, Colorado. Despite the challenges of a relatively large-scale renewable energy project, it was an incredible pleasure beginning to end, given the stunning beauty of the location and contagious energy of the tireless individuals who were as eager to dig a seventy five foot trench as they were to learn hands-on about electrical wiring.

Twenty four, four foot deep holes filled with concrete provide the foundation to six aluminum frames which hold four panels each. We rewired three electrical boxes, migrating mission critical circuits (ie: lights, outlets, water pump, refrigerator) to the panel which is now isolated from the grid and powered by the battery-backed inverter. Best of all, there is ample power for the hot tub.

At 8,000 feet the ranch is surrounded by ten thousand foot peaks, undulating hilltops and ravines which harbor horses, deer, coyotes, bear, and buffalo. Any sense of guilt at having enjoyed such a job site is completely washed away when I consider that the power required to heat the hot tub is more than offset by the new solar PV array.

The introduction of a passive solar water heater would certainly be more efficient than converting sunlight to electricity which in turn heats the water, but as with most adoptions of technology, change is best taken one step at a time. This is true not only on the small scale of one ranch in the middle of thousands in Colorado, but also for the worldwide effort to transition to renewable energy.

Too often I hear the argument that we will never be able to rely entirely upon renewable energy sources, that the efficiency of solar panels and wind turbines is simply not high enough to produce the power required.
This skepticism is parallel to the naysayers of so many human achievements—and a failure to recognize the relatively brief history of research and the commercial application to renewable energy. As with all evolving technologies, renewable energy will not achieve full market play until market demand and the resulting mass production forces a higher level of efficiency. In this case “grid parity,” or the ability to produce energy for the same or lower cost than traditional methods such as coal, nuclear, or gas. The good news is that we have achieved this in certain markets, and are moving to find grid parity in a greater diversity of regions.

The history of photovoltaic energy production goes back to 1883 where Charles Fritts created a solar cell which converted just one percent of sunlight into electricity. In the late 1960s Elliot Berman and an Exxon research team increased the power-to-cost ratio by five fold in just two years. Fast forward and solar cells are manufactured today for roughly $1 per watt, compared to $250 in 1954. A two hundred and fifty times reduction in the cost of manufacturing in roughly sixty years without a market nearly as substantial as the housing, automobile, or even bicycle industries.

So what is holding solar power back?

I will not dive into the politics of renewable energy, for that alone could fill a few columns. At a lightly technical level there are some hurdles which have only recently been surmounted. The entry at wikipedia.org/wiki/Solar_cell provides an in-depth journey through the history and technology of the photovoltaic principal. The basic concept, however, is this: humans see what we call the visible portion of the spectrum while silicon-based solar cells are able to convert only a portion of that light energy into electricity. While the visible spectrum represents a good bit of the energy produced by the sun, this does not constitute the full energy available for conversion to electricity.

We are missing the tremendous potential for conversion of infrared and ultraviolet light energy. Relatively recent research into combinations of elements to expand the sensitivity of the solar cell has increased the efficiency of energy conversion.

In our own backyard, the National Renewable Energy Lab is researching cells with upwards of 40% efficiency, more than forty times greater than the original solar cell just 150 years ago. While southern California and Hawaii have achieved grid parity using traditional silicon based solar cells at efficiencies at or below 20%, the near-future potential for doubling this efficiency lies in the ability to reduce cost of production, the result being that multi-spectral systems are available to you, me, and those who have solar powered hot tubs in the mountains of Colorado at a market friendly price.

Until that time, I am pleased to sit back after a hard day’s work and know that the warm water which gives me comfort was generated, even if indirectly, by energy from the sun. I believe the near-future holds an exciting, rapid evolution for renewable energy production, soon becoming something greater than an alternative, rather, simply the way it is done.